Laser processing device, processing method, and method of producing circuit substrate using the method

ABSTRACT

A laser processing apparatus for performing processing such as perforation on a ceramic green sheet etc. using a laser beam efficiently. The laser processing apparatus is provided with a plurality of optical path systems disposed between a laser oscillator and an irradiation position control optical system for irradiating a predetermined position on a work piece with a laser beam. The plurality of optical path systems includes an optical path system that guides the laser beam to the irradiation position control optical system without changing its cross sectional shape in the direction perpendicular to the optical axis of the laser beam and an optical path system that guides the laser beam while changing its cross sectional shape so that these optical path systems are selectively used in accordance with the processing condition.

TECHNICAL FIELD

The present invention relates to a processing apparatus and processingmethod for performing a processing such as perforation or cutting on awork piece using a laser beam. More particularly, the present inventionrelates to a perforation apparatus and perforation method forefficiently perforating a so-called ceramic green sheet made of aceramic and a method for manufacturing a circuit board by processing thegreen sheet.

BACKGROUND ART

Circuit boards made of a ceramic have superior heat-resisting qualityand durability as compared to general resin boards, and their use in,for example, personal digital assistants have been increasing. On theother hand, with a view to increase packing densities, cases in whichfunctions as a circuit are added to ceramic boards and such boards arestacked to be used as a multilayer board have also been increasing. Thegreen sheet is a common name for a ceramic etc. before sintering, andthe board is generally subjected to processing such as perforation forforming multilayer wiring in the green sheet state.

Use of a laser beam in perforation or other processing has beenincreasing in view of the processing rate achieved or the facility inchanging the shape of the processed hole or in view of easiness informing a hole with a high circularity. In the following, a conventionalapparatus for perforating various work pieces, especially ceramic greensheets using a laser beam will be briefly described with reference toFIG. 6.

This apparatus includes a laser oscillator 101 for generating a laserbeam used for processing, a guide laser oscillation apparatus 102 forgenerating a guide laser beam, an optical system 120 for shaping theguide laser beam and the processing laser beam and guiding them to apredetermined position on a work piece 103, an XY stage 104 for movingthe work piece 103 placed on it in the X and Y directions, a camera 105for capturing the shape of the guide laser incident on the work piece103 or the shape of a processed hole etc. as an image and used forpositioning of the work piece, and a control system 110 for drivingthese components. The guide laser (for example, red light) is projectedonto the work piece previously, so that correction of the position atwhich the laser for actual processing is projected or correction of theshape of the laser is effected based on the projection position andshape of the guide laser.

The optical system 120 is composed of total reflection mirrors 121, 123,126, a dichroic mirror 122, a mask 124, a collimator lens 127, an XYgalvano scanner mirror 128 and an fθ lens 129. The laser beam emittedfrom the laser oscillator 101 is deflected by the total reflectionmirror 127 so as to be directed toward the dichroic mirror 122, andtransmitted through the dichroic mirror 122 from its back side. Then,the laser beam is deflected again by the total reflection mirror 123 soas to be directed toward the mask 124. The guide laser beam emitted fromthe guide laser oscillator 102 is deflected by the dichroic mirror 122so as to travel on the same optical path as the processing laser beam.

The processing laser beam and the guide laser beam pass through theopening 124 a of the mask 124, whereby they are shaped into a formcorresponding to a hole to be formed such as a approximately circularform etc. The laser beam after transmitted (passing) through the mask isa little divergent, and it is necessary to reshape it into parallellight using a collimator lens or the like. For this purpose, the laserbeam after shaping is deflected by the total reflection mirror 126 so asto enter the collimator lens 127. The irradiation position of the laserbeam having been made into parallel light by the collimator lens 127 ismoved by the XY galvano scanner mirror 128 and the fθ lens 129 in such away that it is delivered to a desired processing position on the workpiece 103. The XY galvano scanner mirror 128 and the fθ lens 129function together as an irradiation position control optical system forthe laser beam.

The control system 110 is composed of a galvano scanner control portion112, an image processing portion 113, a drive control portion 114 and amain control portion for controlling these portions and controlling thelaser oscillator etc. in synchronization with the control by theseportions. The galvano scanner control portion 112 is connected with theXY galvano scanner mirror 128 to control the irradiation position of thelaser beam by controlling the XY galvano scanner mirror 128. The imageprocessing portion 113 is connected with the camera 105. The imageprocessing portion 113 monitors the condition, position and degree ofaccuracy of the processed hole based on an image obtained through thecamera 105 and outputs information on the number of pulses and intensityof the laser beam to the main control portion. The drive control portion114 drives the XY stage 104 to change the position of the work piece 103in such a way that the position on the work piece at which a hole is tobe made comes into the area that can be irradiated by the laser beamcontrolled by the galvano scanner mirror. This apparatus is constructedin such a way that the shape of the mask 124 is projected onto thesurface of the work piece 103 at a desired reduction ratio, and aprocessed hole with a nearly circular shape and having little taper inits cross section is obtained.

In the above-described conventional apparatus, a large part of the laserbeam is blocked by the mask 124, and only the portion that have passedthrough the opening 124 a of the mask is used for actual processing.Accordingly, the utilization efficiency of the laser beam is not sohigh, and it is required to use an oscillator having a relatively largeoutput power as the laser oscillator 101 in view of the aforementionedblocking. It is considered that the utilization efficiency of the laseraffects the processing efficiency greatly especially in the case thatthe surface layer is made of a material having a relatively lowabsorption efficiency for the laser beam. In this case, the number ofpulses of the laser required for processing is very large, which resultsin a large decrease in the processing efficiency.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above-describedproblems. An object of the present invention is to improve theutilization efficiency of the laser beam and to enhance the processingefficiency even for work pieces with a surface made of a material thatis hard to process, to provide a laser processing apparatus and aprocessing method with which a desired processed shape can be easilyachieved. Another object of the present invention is to provide a methodfor manufacturing a circuit board in which processing such asperforation is applied on a ceramic green sheet using the aforementionedmethod.

To solve the above-described problems, according to the presentinvention, there is provided a laser processing apparatus forirradiating a work piece with a laser beam to process the irradiatedportion comprising a laser oscillator for generating the laser beam, anirradiation position control optical system for causing the laser beamto irradiate a predetermined position on the work piece, and a pluralityof optical path systems for guiding the laser beam emitted from thelaser oscillator to the irradiation position controlling optical system,wherein the plurality of optical path systems includes at least a firstoptical path system that guides the laser beam emitted from the laseroscillator to the irradiation position control optical system withoutchanging the energy distribution in the direction perpendicular to theoptical axis of the laser beam and a second optical path system thatguides the laser beam emitted from the laser oscillator to theirradiation position control optical system while changing the energydistribution in the direction perpendicular to the optical axis of thelaser beam.

To solve the above-described problems, according to the presentinvention there is provided a laser processing apparatus for irradiatinga work piece with a laser beam to process the irradiated portioncomprising a laser oscillator for generating the laser beam, anirradiation position control optical system for causing the laser beamto irradiate a predetermined position on the work piece, and a pluralityof optical path systems for guiding the laser beam emitted from thelaser oscillator to the irradiation position controlling optical system,wherein the plurality of optical path systems includes at least a firstoptical path system that guides the laser beam emitted from the laseroscillator to the irradiation position control optical system withoutchanging the energy intensity of the laser beam and a second opticalpath system that changes the energy distribution in the directionperpendicular to the optical axis thereof by preventing a portion of thelaser beam emitted from the laser oscillator from reaching theirradiation position control optical system.

The above-described apparatus may include optical path switching meansfor switching the optical path that is used in guiding the laser beam,and the switching of the optical path systems may be performed during anoff-time of the pulse irradiation of the laser beam. Furthermore, in theabove-described apparatus, the second optical path system that changesthe energy distribution of the laser beam may include a mask orhomogenizer or a combination of them that makes the energy distributionin the direction perpendicular to the optical axis of the laser beamsubstantially uniform.

To solver the above-mentioned problems, according to the presentinvention, there is provided a laser processing method for irradiating awork piece with a laser beam to process the irradiated portion,comprising a first processing step of irradiating a predeterminedposition on the work piece with a laser beam emitted from a laseroscillator without changing its energy distribution in the directionperpendicular to the optical axis of the laser beam, a laser beamswitching step of stopping the irradiation with the laser beam that isnot changed in its energy distribution and guiding a laser beam that isformed by changing the energy distribution in the directionperpendicular to the optical axis, of the laser beam emitted from thelaser oscillator to the predetermined position on the work piece, and asecond processing step of performing irradiation with the laser beamthat has been changed in the energy distribution.

In the above-described method, it is preferable that the laser beamswitching step be performed during an off-time of the pulse irradiationof the laser beam emitted from the laser oscillator. It is alsopreferable that the energy intensity distribution of the laser beam thathas been changed in the energy distribution guided onto the work piecebe made uniform.

To solve the above-mentioned problems, according to the presentinvention, there is provided a method of manufacturing a circuit boardcomprising a step of performing a perforation processing on a ceramicgreen sheet and a step of filling the hole formed with an electrodematerial, the perforation processing comprising a first processing stepof irradiating a predetermined position on the ceramic green sheet witha laser beam emitted from a laser oscillator without changing its energydistribution in the direction perpendicular to the optical axis of thelaser beam, a laser beam switching step of stopping the irradiation withthe laser beam that is not changed in its energy distribution andguiding a laser beam that is formed by changing the energy distributionin the direction perpendicular to the optical axis, of the laser beamemitted from the laser oscillator to the predetermined position on thework piece and a second processing step of performing irradiation withthe laser beam that has been changed in the energy distribution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the basic structure of a laser processingapparatus according to an embodiment of the present invention.

FIG. 2 schematically shows the basic structure of the second opticalpath system shown in FIG. 1.

FIG. 3 illustrates the optical path switching mirror in FIG. 1.

FIGS. 4A, 4B, 4C, 4D and 4E show sequential statuses of processing inthe case of a conventional apparatus.

FIGS. 5A, 5B, 5C, 5D and 5E show sequential statuses of processing inthe case of an apparatus according to the present invention.

FIG. 6 schematically shows the basic structure of a conventional laserperforating apparatus.

THE BEST MODE FOR CARRYING OUT THE INVENTION

A laser processing apparatus according to an embodiment of the presentinvention will be described in detail with reference to the drawings. Inthis apparatus, the portions other than the optical system, namely thelaser oscillator, the guide laser oscillator, the XY stage and thecontrol portions etc. are not particularly different from those in theconventional apparatus, and the following description will be mainlydirected to the optical system. FIG. 1 shows the outline of the opticalsystem in the processing apparatus according to the present invention.This optical system includes total reflection mirrors 21 and 26, adichroic mirror 22, optical path switching mirrors 8 and 9, a firstoptical path system 30 and a second optical path system 40.

A processing laser beam emitted from the laser oscillator 1 is deflectedby the total reflection mirror 21 toward the dichroic mirror 22,transmitted through the dichroic mirror 22, and then arrives at theposition of the optical path switching mirror 8. A guide laser beamemitted from the guide laser oscillator 2 is deflected by the dichroicmirror 22 so that its optical path will coincide with that of theprocessing laser beam. Which optical path system, among the firstoptical path system 30 and the second optical path system 40, theprocessing laser beam and the guide laser beam is made to pass isselected by the optical path switching mirror 8.

The laser beam having passed through the first or second optical path30, 40 is reflected by the optical path switching mirror 9 toward thetotal reflection mirror 26, and directed by this mirror to a collimatorlens that is not show in the drawings. In the downstream of thecollimator lens, an XY galvano scanner mirror and other parts similar tothose in the conventional apparatus are provided, and the laser beam isguided to a desired position on the work piece by those opticalelements. In other words, the laser processing apparatus according tothe present invention is provided with an irradiation position controloptical system including the XY galvano scanner mirror etc., though theyare not shown in FIG. 1.

The first optical path system 30 includes total reflection mirrors 31and 32 and a beam expander 35. In this optical system, the laser beamarrives at the expander 35 without being blocked by any means. Theirradiation diameter of the laser beam is enlarged by the expander sothat a predetermined area can be irradiated with the laser beam, andthen the laser beam is guided to the optical path switching mirror 9. Nostructure that may partially block the laser beam is disposed in theoptical path of the laser beam passing through the first optical pathsystem 30. Therefore, it is possible to make the most part of theprocessing laser emitted from the laser oscillator 1 to be incident onthe work piece directly.

In other words, the energy intensity of the laser beam directed to thework piece through the first optical path system 30 is not reduced fromthe state as it was when emitted from the laser oscillator, and theenergy distribution in the direction perpendicular to its optical axis(the cross sectional shape) does not vary. Accordingly, processing withhigh utilization efficiency can be realized. In connection with this, ifthe energy density of the laser beam delivered to the surface of thework piece is to be enhanced further, a condenser lens or the like maybe used in place of the aforementioned beam expander. In this case also,the total energy of the laser beam in the direction perpendicular to theoptical axis does not vary, and similarity of the energy distribution isalso maintained basically.

The second optical path system 40 includes a homogenizer 45, a slit 44and total reflection mirrors 41 and 42. In this optical path system, theoutput waveform of the laser beam is shaped by the homogenizer 45 insuch a way that the energy distribution of the laser beam becomes atop-hat shape. FIG. 2 schematically shows the beam shaping effected bythe homogenizer. The beam waveform (i.e. the energy distribution) shownwith respect to the direction perpendicular to the traveling directionof the laser beam is of the shape indicated by Ein in FIG. 2. When thelaser beam passes through two aspherical lenses 45 a and 45 b havingcertain curved surfaces included in the homogenizer 45, the laser lightcorresponding to the central portion of Ein is dispersed to theperipheral portions and the laser light corresponding to the peripheralportions is concentrated to the central portion. As a result, the laserbeam emerging from the homogenizer 45 will have a beam shape calledtop-hat indicated by Eout in which an energy intensity distribution issubstantially uniform all over the irradiation area. Thus, the energydistribution in the direction perpendicular to the optical axis of thelaser beam having passed through the second optical path system 40 hasbeen deformed to a large extent as compared to the distribution justafter the laser beam is emitted from the oscillator.

The laser beam that has been shaped into the top-hat by the homogenizer45 passes through a mask 44 disposed in the downstream of thehomogenizer, whereby the laser beam is shaped to have a beam shapecorresponding to the opening 44 a. The laser beam thus shaped is guidedby the total reflection mirrors 41 and 42 to the optical path switchingmirror 9, and then it is guided by the total reflection mirror 26 to thecollimator lens not shown in the drawings in the same manner as thelaser beam having passed through the first optical path system 30. Asper the above, for example in the case that a nearly circular hole is tobe formed on a work piece, it is possible to produce a laser beam havinga circular shape and having a uniform beam intensity in the circulararea by passing the laser beam through the homogenizer 45 and the mask44.

Next, the optical path switching mirrors 8 and 9 will be described indetail with reference to FIG. 3. FIG. 3 shows the optical path switchingmirror 8, and the following description will be directed only to themirror 8, since the basic structure thereof is the same as the mirror 9.The mirror 8 is connected, at its back side end, with a drive apparatussuch as a single axis drive motor and a cylinder etc. not shown in thedrawings. The mirror 8 is adapted to be driven in a specific axialdirection A, and it can be stopped at two positions, one of which is inthe optical path of the laser beam and the other is out of the opticalpath. When the laser beam reflection surface 8 a is out of the opticalpath, the laser beam is guided to the first optical path system withouta change in its traveling direction. On the other hand, when thereflection surface 8 a is in the optical path, the traveling directionof the laser beam is changed by the reflection surface by 90 degrees andguided to the second optical path system.

By using the laser processing apparatus having the above-describedstructure, it is possible to improve the utilization efficiency of thelaser beam and to enhance the processing efficiency even for work pieceswith a surface made of a material that is hard to process, and thereforea desired processed shape can be easily obtained. In the following,advantages of the present invention will be described in connection witha specific case in which perforation processing is performed on a workpiece having the first layer that is hard to process and the secondlayer that is easy to process, with reference to sequential statuses inthe case of the processing by the conventional apparatus shown in FIGS.4A, 4B, 4C, 4D and 4E and sequential statuses in the case of theprocessing by the apparatus according to the present invention shown inFIGS. 5A, 5B, 5C, 5D and 5D.

FIGS. 4A, 4B, 4C, 4D and 4E and FIGS. 5A, 5B, 5C, 5D and 5D show casesin which a hole is made on a work piece in which the second layer 62that is easy to process and the first layer 61 that is hard to processare laminated on a base film 60 made of a PET or the like, while thebase film 60 is left unprocessed. In the case that the laser beam thathas been shaped by a mask or the like is used, a hole is formed in thelaser beam irradiation area on the first layer 61 from its outermostsurface at a substantially constant processing rate as shown in FIGS.4B, 4C and 4D. In this case, since the energy density of the laser beamper unit irradiation area is low, the hole formation speed is low.Accordingly, the required number of pulses of the irradiation laser beamis very large. After the first layer 61 that is hard to process has beenremoved, the perforation processing is applied on the second layer 62that is easy to process, as shown in FIGS. 4D and 4E, and the number ofirradiation pulses can be made small.

In the case that the laser processing apparatus according to the presentinvention is used, the surface of the first layer 61 is firstlyirradiated with the laser beam having passed through the first opticalpath system. In this case, the laser beam is delivered to the surface ofthe work piece while having, for example, a Gaussian distribution inwhich the energy density is high at its center without a loss in itsenergy. Accordingly, a hole is formed rapidly at the substantiallycentral portion of the laser beam irradiation area as shown in FIG. 5B.However, the laser beam used has not been subjected to any shapingprocess as to its shape and energy distribution etc. Therefore, if theprocessing is further performed with this laser beam, it is difficult toproduce a hole with a desired shape. In view of this, at the time when apart of the first layer 61 is thoroughly removed and a portion of thesecond layer 62 is exposed in the laser beam irradiation area, the laserbeam used is switched to the laser beam having passed through the secondoptical path system that has been shaped and rendered uniform (FIG. 5C).The switching operation is effected by the optical path switchingmirrors 8 and 9.

At the time when the laser beam is switched, the first layer 61 that ishard to process still remains in the laser irradiation area to someextent. Accordingly, after the laser beam has been switched, theprocessing rate differs between in the vicinity of the outer peripheryof the irradiation area and in the vicinity of the center, and the crosssectional shape of the hole made is tapered as shown in FIG. 5C or 5D.However, the taper can be eliminated by optimizing the number of pulsesof the irradiation laser beam etc. to terminate the perforationprocessing at the base film 60 and removing the vicinity of theperiphery of the irradiation area by subsequent laser beam irradiation.

With the above-described process shown in FIGS. 5A, 5B, 5C and 5D, it ispossible to make a hole without a taper in its cross section similar tothe hole shown in FIG. 4D produced by the conventional apparatus. Inaddition, by carrying out the present invention, it is possible toreduce the time taken from the surface of the first layer 61 isirradiated with the laser beam until the laser beam reaches the secondlayer. Thus, the productivity of the laser processing apparatus can beenhanced. Furthermore, even if the processing rate with the laser beamhaving passed through the second optical path is decreased for examplewith adaptation of this laser beam to more precise shapes etc., it ispossible to make a hole such as one having a nearly circular openingwith an improved precision at a rate equal to or more than in the caseof the conventional apparatus, since the processing rate is increased bythe laser beam having passed through the first optical path system.

The multilayer structure described heretofore includes, for example, astructure in which a metal electrode layer is formed on the outermostprocessed surface and a ferrite-based or alumina-base ceramic layer isformed under it. It is considered that the present invention iseffectively applied to the case where perforation processing is appliedto a sheet made of a single layer of an alumina-based ceramic that isconsidered to be hard to process with a laser beam. In this case also,it is preferable to form a hole on the sheet using the laser beam havingpassed through the first optical path system and to subsequently shapethe hole using the laser beam having passed through the second opticalpath system by following the process similar to the process of switchingthe optical path described in the foregoing.

In the above description of the embodiment, parameters related to theprocessing conditions such as the energy density, the irradiation timeand the number of pulses of the laser beam have not been described forthe sake of simplicity of the description. However, by controlling theseparameters in addition to the switching of the optical path system, itis possible to form a hole having a desired depth or a tapered shape.The present invention is considered to be effective especially in thecase that the energy or the pulse energy of the laser emitted from theoscillator is low, and the invention is especially effective in the casethat a high-order harmonics laser of the UV range is used as well as inthe case of a CO2 laser or a YAG laser is used.

Although in this embodiment a homogenizer 25 serving as a beam shapingelement is provided between the optical path switching mirror 8 and themask 44, it may be eliminated if the range of the variation of theenergy distribution in the irradiation area meets a desired level. Inthis embodiment, with the provision of this element, processing using alaser beam having an improved top-hat energy distribution is madepossible, and it is possible to form a hole with little taper in itsshape. Holes having such a shape are suitable for the case whereperforation processing is applied to a sheet with the ceramic portionhaving a thickness of 30μ or less, or in the case where a hole formed isto be filled with an electrode material or the like and the viscosity ofthe filler paste is as small as 50 Pa·s or less.

Furthermore, it is possible to form a desired beam by changing thecurvature, refractive index or other factors of the aspherical lensesthat constitutes the homogenizer. Therefore, it is also possible tocontrol the taper in cross section of the processed hole by preparingmultiple types of homogenizers in advance and setting them on theoptical axis as needed. Such holes the taper of which is controlled aresuitable for the case where the diameter of the hole relative to thethickness of the green sheet (or the aspect ratio) is large or in thecase where a hole formed is to be filled with an electrode material orthe like and the viscosity of the filler paste is as large as 200 Pa·sor more.

In the above-described embodiment, a total reflection mirror are usedfor switching of the optical path. In this switching method, it ispreferable that the mirror be moved at a speed synchronized with thelaser irradiation pulse. Specifically, it is preferable that the mirrorbe driven in response to the off-state of the laser beam in the pulseirradiation at such a speed that the movement of the mirror into or outof the optical path is completed during the off-state or off-time. Inthis case, it is more preferable that the apparatus be constructed insuch a way that the mirror or the like is driven in some correlationwith the pulse, for example, in such a way that the mirror is driven insynchronization with the moment at which the laser irradiation changesto the off-state or that the driving of the mirror is completed apredetermined time before the laser irradiation changes to the on-state.This enables continuous switching of the optical path and realizes animprovement in the processing efficiency.

Although in the above-described embodiment, a mirror that moves alongone axis is used for switching the optical path, this feature is notessential to the invention. The switching of the optical path may becarried out, for example, by providing a so-called chopper having adisk-like shape in which surfaces with a mirror and surfaces without amirror are alternately disposed and rotating it. Alternatively, theswitching of the optical path may be done by providing a half mirrorthat transmits 50% of the light quantity in place of the totalreflection mirror and providing shutters or the like in the respectiveoptical paths in the downstream of the half mirror, and opening/closingthe shutters. The speed of opening/closing of the shutters can be madehigher than the speed of the direct driving of the mirror, and thereforemore speedy switching of the optical path can be made possible. Inaddition, in this case, by changing the ratio of the reflection andtransmission of the half mirror in a desired manner, it is possible toperform processing such as perforation in a condition more suitable forthe characteristics of the work piece.

Although there are two optical path systems in the above-describedembodiment, the present invention is not limited to this feature, but anadditional optical path system may be introduced. In connection withthis, for example, an optical path system similar to the first opticalpath system but having no expander may be added. With this optical pathsystem, a laser beam having a higher energy intensity in the centralportion of the laser beam irradiation area can be produced.Alternatively, an optical path system similar to the second optical pathsystem that is modified to be able to produce a laser beam in which theenergy intensity in the vicinity of the periphery of the laser beamirradiation area is enhanced by means of a homogenizer may be added.Alternatively, a plurality of optical path system corresponding todifferent beam shapes may be provided so that a desired optical path isselected from them in accordance with the characteristics of the workpiece or the required processed shape etc.

In the above-described embodiment, the processing using the secondoptical path system is effected after completion of the perforationprocessing using the first optical path system. However, this feature isnot essential to the present invention. For example, the perforatingoperations using the first optical path system and the second opticalpath system respectively may be performed repeatedly for several numberof pulses. Furthermore, the ratio of the periods over which therespective optical path systems are used may be changed as needed inaccordance with the status of the processing or the precision of thehole shape etc.

Although the above description of the embodiment has been directedmainly to perforation processing applied to a ceramic green sheet or thelike and a process of manufacturing a circuit board using theprocessing, the application of the processing according to the presentinvention is not limited to them. Objects to be processed may bearticles made of various materials such as metals or resins or articlesincluding multiple layers of these materials. Application of the presentinvention is not limited to a perforation process, but it may also beapplied to various process, such as a cutting process or a patternmodification process, in which an improvement in processing speed orprocessing precision can be expected by selectively using a laser beamhaving a relatively high intensity and a laser beam that has beenshaped.

By carrying out the present invention, it is possible to performprocessing such as perforation on a ceramic green sheet or the likewhile using a laser beam efficiently. In addition, by using laser beamshaving different beam shapes as desired, it is possible to improve theprocessing efficiency in processing a work piece having a surface madeof a material that is hard to process, and a desired processed shape canbe easily obtained.

1. A laser processing apparatus for irradiating a work piece with alaser beam to process the irradiated portion comprising: a laseroscillator for generating said laser beam with a predetermined pulse; anirradiation position control optical system for causing said laser beamto irradiate a predetermined position on said work piece; a plurality ofoptical path systems for guiding the laser beam emitted from said laseroscillator to said irradiation position controlling optical system; anda total reflection mirror as an optical path switch, which is capable ofproceeding into and retracting from an optical path, for determiningwhich optical path system is used, from said plurality of optical pathsystems, wherein said plurality of optical path systems includes (1) atleast a first optical path system that guides said laser beam emittedfrom said laser oscillator to said irradiation position control opticalsystem without changing its energy distribution in the directionperpendicular to the optical axis of the laser beam and (2) a secondoptical path system that guides said laser beam emitted from said laseroscillator to said irradiation position control optical system whilechanging its energy distribution in the direction perpendicular to theoptical axis of the laser beam, and said total reflection mirror movesinto and retracts from the optical path during an off-time of the laserbeam in the predetermined pulse of said laser oscillator such that saidtotal reflection mirror begins being driven for the moving into andretracting from the optical path when the predetermined pulse of saidlaser beam changes to an off-state, and driving of said total reflectionmirror for the moving into and retracting from the optical path iscompleted before the predetermined pulse of said laser beam changes toan on-state.
 2. A laser processing apparatus for irradiating a workpiece with a laser beam to process the irradiated portion comprising: alaser oscillator for generating said laser beam; an irradiation positioncontrol optical system for causing said laser beam to irradiate apredetermined position on said work piece; and a plurality of opticalpath systems for guiding the laser beam emitted from said laseroscillator to said irradiation position controlling optical system; anda total reflection mirror as an optical path switch, which is capable ofproceeding into and retracting from an optical path, for determiningwhich optical path system is used, from said plurality of optical pathsystems, wherein said plurality of optical path systems includes (1) atleast a first optical path system that guides said laser beam emittedfrom said laser oscillator to said irradiation position control opticalsystem without changing the energy intensity of the laser beam and (2) asecond optical path system that changes the energy distribution in thedirection perpendicular to the optical axis thereof by preventing aportion of the laser beam emitted from said laser oscillator fromreaching said irradiation position control optical system, and saidtotal reflection mirror moves into and retracts from the optical pathduring an off-time of the laser beam in the predetermined pulse of saidlaser oscillator such that said total reflection mirror begins beingdriven for the moving into and retracting from the optical path when thepredetermined pulse of said laser beam changes to an off-state, anddriving of said total reflection mirror for the moving into andretracting from the optical path is completed before the predeterminedpulse of said laser beam changes to an on-state.
 3. A laser processingapparatus according to claim 1 or 2, wherein the second optical pathsystem that changes the energy distribution of said laser beam includesa mask that makes the energy distribution in the direction perpendicularto the optical axis of the laser beam substantially uniform.
 4. A laserprocessing apparatus according to claim 3, wherein the second opticalpath system that changes the energy distribution of said laser beamincludes a homogenizer that makes the energy distribution in thedirection perpendicular to the optical axis of the laser beamsubstantially uniform.
 5. A laser processing method for irradiating awork piece with a laser beam to process the irradiated portion,comprising: a first processing irradiating a predetermined position onsaid work piece with a laser beam emitted from a laser oscillatorwithout changing its energy distribution in the direction perpendicularto the optical axis of said laser beam; a laser beam switching a laserbeam to be used after completing said first processing step, from saidlaser beam that is not changed in its energy distribution to a laserbeam that is formed by changing the energy distribution in the directionperpendicular to the optical axis, of the laser beam emitted from saidlaser oscillator, by moving a total reflection mirror into andretracting said total reflection mirror from an optical path of saidlaser beam during an off-time of the laser beam in the predeterminedpulse of said laser oscillator such that said total reflection mirrorbegins being driven for the moving into and retracting from the opticalpath when the predetermined pulse of said laser beam changes to anoff-state, and driving of said total reflection mirror for the movinginto and retracting from the optical path is completed before thepredetermined pulse of said laser beam changes to an on-state; and asecond processing performing irradiation with said laser beam that hasbeen changed in the energy distribution onto said predetermined positionon said work piece.
 6. A method according to claim 5, wherein the energyintensity distribution of said laser beam that has been changed in theenergy distribution guided onto said work piece is made uniform.